This invention relates to an automatic exposure adjustment circuit in a television camera, which adjusts the video signal output voltage according to the luminance of an object to be photographed. The invention is intended to continuously set an exposure value for an object which the photographer wishes to photograph independently of the ambient light conditions.
In a conventional television camera, exposure adjustment is effected according to the brightness of an object to be photographed, in a method which will be briefly described with reference to FIG. 1. The image of an object to be photographed is converted into an electrical signal by an image pickup element 1. Since the electrical signal is weak, it is amplified by a video amplifier 2. The voltage level of the signal thus amplified is detected by a level detector 3. In the case where the image pickup element 1 is a vidicon, the target voltage, i.e. the voltage applied to the pick-up, is varied by an exposure control circuit (or an ASC circuit) 4 with the aid of the aforementioned voltage, to vary the photoelectric conversion characteristics, whereby the exposure control is carried out to provide a satisfactory image at all times. In the case where the image pickup element 1 is a Saticon, the exposure control is effected by varying the opening of the stop in the optical system. However, those conventional methods are disadvantageous in that, in the case of back lighting or in the case where a bright spot is included in an image plane, the exposure is determined from the luminance of the bright spot (instead of the luminance of an object to be photographed), and accordingly the object appears dark.